Carbon Nanotube Battery Promises to Boost Power, Energy Storage

Researchers at the Massachusetts Institute of Technology (MIT) have developed a lithium-ion battery with a positive electrode made of carbon nanotubes that delivers 10 times more power than a conventional battery and can store five times more energy than a conventional ultracapacitor, according to MIT's Technology Review.

Because lithium-ion battery electrodes made from carbon nanotubes offer high surface area and high conductivity, they could improve energy and power density over conventional forms of carbon. But working with the material has proved challenging because most methods for assembling carbon nanotubes require a binding agent that lowers the conductivity of the electrode and leads to the formation of clumps of material that reduce the surface area. In contrast, the electrodes made by chemical engineering professor Paula Hammond and mechanical engineering professor Yang Shao-Horn have a high surface area for storing and reacting with lithium. Because lithium is stored on the surface, it can move in and out of the electrode rapidly, accelerating battery charging and discharging.

The MIT researchers' electrode assembly process creates dense, interconnected, porous carbon-nanotube films that do not require fillers. The scientists begin the process by creating water solutions of carbon nanotubes with positively and negatively charged groups. Then, they dip a substrate into the two solutions, causing the nanotubes, attracted by differences in their charge, to cling to one another in uniform, thin layers. When they are heated and removed from the substrate, these films can store a great amount of charge and release it quickly, acting like an electrode in an ultracapacitor.

In an article in the journal Nature Nanotechnology, the MIT team demonstrates that lithium ions in a battery electrolyte react with oxygen-containing chemical groups on the surface of the carbon nanotubes in the film. Because of the large surface area and porous structure of the nanotube electrodes, there are many places for the ions to react. They can also travel in and out rapidly, giving the nanotube battery high energy capacity and power, Shao-Horn says.